A thermoplastic resin can have improved properties such as lower specific gravity than glass or metal and improved formability, impact resistance, and the like. Recently, thermoplastic resins have been used to manufacture plastic products, as electric/electronic products are becoming less expensive and also larger and lighter. The plastic products have rapidly replaced conventional glass or metal products and have been widely used in a variety of products, from electric/electronic products to auto parts.
There is also an increasing demand for light weight unpainted materials for auto materials to save energy and provide environmental friendliness. When an unpainted material is used as an auto exterior material, the unpainted material does not need to be painted using conventional painting processes and thus, can be environmentally-friendly and less expensive. Such unpainted materials, however, require high coloring properties and also weather resistance against outdoor temperature and moisture and scratch resistance against an external impact or chip.
Conventionally, auto exterior materials include an acrylate-styrene-acrylonitrile copolymer (ASA) resin, which can have improved weather resistance as compared to a conventional acrylonitrile-butadiene-styrene copolymer (ABS) resin. The ASA resin can maintain the properties of the ABS resin and have improved weather resistance by using an acrylic-based impact-reinforcing agent (g-ASA) with no double bond (that has poor weather resistance). The ASA resin, however, can exhibit deteriorated coloring properties and scratch resistance, which are caused by the low refractive index of the acrylic-based impact-reinforcing agent. The ASA resins can be difficult to use as a high gloss and unpainted material.
In contrast, an acrylic-based resin represented by a polymethylmethacrylate (PMMA) resin can have improved transparency, weather resistance, mechanical strength, surface gloss, adherence, and the like and particularly, very improved scratch resistance. PMMA resins, however, can have very weak impact resistance and thus may not be appropriately used as an auto exterior material.
The impact resistance of the acrylic-based resin having improved coloring properties, weather resistance, and scratch resistance may be increased by using a transparent acrylic-based impact-reinforcing agent having a similar refractive index to that of the acrylic-based resin. See, for example, Korea Patent Nos. 1999-7011551 and 2003-0053711.
However, when such a transparent acrylic-based impact-reinforcing agent is used to increase impact resistance, the impact improvement effect can be lowered due to the transparent acrylic-based impact-reinforcing agent having lower impact efficiency than a butadiene-based impact-reinforcing agent. For example, when a transparent acrylic-based impact-reinforcing agent prepared using an acrylic-based monomer and a styrene monomer in a core and an acrylic-based monomer in a shell to match the refractive index of the acrylic resin is used with the acrylic-based resin, the impact reinforcement effect can be relatively lower than the acrylic-based impact-reinforcing agent (g-ASA) for ASA.
In addition, the transparent acrylic-based impact-reinforcing agent can deteriorate heat resistance or mechanical properties and scratch resistance when its amount is increased and thus, has a limit in improving impact strength.
According to another method, the transparent acrylic-based impact-reinforcing agent may be used with a butadiene-based impact-reinforcing agent in a small amount to supplement deterioration of impact strength. This, however, can deteriorate weather resistance.